This disclosure is generally directed to radiation curable solid inks, and their use in forming images, such as through transfuse printing. More specifically, this disclosure is directed to radiation-curable solid inks, such as low-shrinkage radiation curable solid inks, that comprise solid monomers and a reactive wax.
Transfuse printing systems are known in the art, and thus extensive description of such devices is not required herein. Solid inks (also referred to as phase change or “hot melt” inks) are desirable for transfuse printing systems because they remain in a solid phase at room temperature during shipping, long-term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the transfuse printing.
Solid inks typically used with transfuse printing systems have a wax-based ink vehicle, for example, a crystalline wax-based ink vehicle. Such solid inks provide vivid color images. In typical systems, the crystalline-wax inks are jetted onto a transfer member, for example, an aluminum drum, at temperatures of approximately 120 to about 140° C. The wax-based inks are heated to such high temperatures to decrease their viscosity for efficient and proper jetting onto the transfer member. The transfer member is typically at a temperature of about 60° C., so that the wax will cool sufficiently to solidify or crystallize. As the transfer member rolls over the recording medium, for example paper, the image comprised of wax-based ink is pressed into the paper.
While currently available ink compositions are suitable for their intended purposes, a need remains for a new type of solid ink that is capable of being printed via the piezoelectric transfuse printing process. There is further a need for ink compositions that can be processed at lower temperatures and with lower energy consumption, have improved robustness, have improved jetting reliability and latitude. In addition, a need remains for a new type of solid ink composition that exhibits desirably low viscosity values at jetting temperatures, generates images with improved look and feel characteristics, generates images with improved hardness and toughness characteristics, and that is suitable for a number of commonly used substrates. There is further a need for a solid ink composition that can ensure, to the extent that toxic or otherwise hazardous compounds are used in such compositions, that migration, evaporation or extraction of such materials from this new type of ink be controlled or ameliorated. When used in certain applications, for example food packaging, it is desirable to reduce the amount of or eliminate altogether extractable species present, for example to meet environmental, health and safety requirements.
The present disclosure, in embodiments, addresses one or more of these needs by providing a radiation curable solid ink composition comprising blends of waxes, resins, monomers, curable waxes, pigments and free-radical photoinitiators.